All planets are not perfectly spherical. They are more accurately described as oblate spheroids. This means they are slightly flattened at the poles and bulging at the equator.

Here's why:

* Rotation: All planets rotate on their axes. This rotation creates centrifugal force, which pushes matter away from the axis of rotation. This force is strongest at the equator, leading to a bulge.

* Gravity: Gravity pulls matter towards the center of the planet. This force is stronger at the poles than at the equator due to the planet's oblate shape.

The degree of oblateness varies depending on the planet's size, rotation speed, and density. For example, Saturn is significantly more oblate than Earth because it rotates much faster and has a lower density.

So, while we often think of planets as spheres, they are actually slightly flattened at the poles and bulging at the equator due to their rotation and gravity.